The present invention generally relates to vehicle convertible roofs, and more particularly to a vehicle convertible roof having a roof bow that is moveable to vary tension of the convertible roof.
Traditional soft-top convertible roofs for automotive vehicles typically employ three, four or five roof bows, having an inverted U-shape spanning transversely across the vehicle for supporting a vinyl, canvas or polyester fabric pliable roof cover. A number one roof bow is mounted to a pair of front roof rails and is typically latched to a stationary front header panel of the automotive vehicle body disposed above the front windshield. A number two roof bow is typically mounted to a pair of center roof rails which are pivotally connected to the front roof rails. Furthermore, a number three, four and any additional optional roof bows are commonly mounted to a pair of rear roof rails which are pivotally coupled to the center roof rails. The roof cover can also have a hard or rigid portion along with the pliable portion. For example, reference should be made to U.S. Pat. No. 5,429,409 entitled xe2x80x9cConvertible Topxe2x80x9d, which is incorporated by reference herein.
The roof cover fabrics are exposed to a full range of weather environments and are expected to maintain their original appearance for several years. Due to these durability requirements, the roof covers are normally quite heavy and multi-layered, such as vinyl on cloth or two layers of cloth with an elastomer interlayer. The technical specifications are quite stringent and the fabrics exhibit relatively little stretch. However, the roof covers relax substantially in the sunshine or hot environments and shrink in cold environments.
To compensate for the relaxing and shrinking of the cover, great care must be taken when designing the cover and the top stack mechanism of the convertible roof to achieve a taut cover surface without wrinkles regardless of the environmental conditions. Furthermore, care must also be taken to achieve such a surface while still permitting easy pull-down and latching (by the driver in the case of a manually operated convertible roof). To achieve this balance, first-time closure efforts often range between 100 to 200 pounds at the factory. After the top stack mechanism remains in the raised position and latched for several days, this effort normally drops to about 30 to 50 pounds, which is considered acceptable. However, if the top stack mechanism remains in the stowed position for a period of several days, it may become difficult to latch on the first cycle because of the tendency of the cover to return to its nominal unstretched dimensions. Various xe2x80x9cstretchablexe2x80x9d roof cover fabrics have been tried without success, thereby increasing the incentive to find a means for optimizing a balance between easy latching and taut appearance while utilizing the present types of fabrics that are employed in the roof covers.
The problem of high latching efforts is caused by the varying tension in the cover material which is acting against the forward movement of the number one roof bow to latch to the stationary front header panel. Force vector analysis indicated that a pull-down force of 20 to 50 pounds at the number one roof bow may be counter balanced with a force of 20 to 50 pounds acting in the plane of the number four roof bow, which yields a force of about 200 pounds in fabric tension of the roof cover. This level of force is adequate for maintaining a taut appearance in a properly fitted roof cover. Thus, if the tension in the roof cover could be limited by making the number four bow adjustable, easy latching can be assured along with a taut appearance.
In accordance with the present invention, a convertible roof system for an automotive vehicle includes a roof bow that is operable between extended and retracted positions to vary tension of the roof cover and is actuated by a link that travels along a camming surface when the folding mechanism supporting the cover moves between the raised and stowed position. In another aspect of the present invention, a latching member is operable to latch an adjustable roof bow in a retracted position and retains the roof bow in the retracted position as the convertible roof system moves from a stowed position to a raised position. In a further aspect of the present invention, a vehicle convertible roof system with an adjustable roof bow uses a multi-link assembly that couples the roof bow to a roof rail. The multi-link assembly includes a first link and a second link that encircles the first link and slides along the first link as the adjustable roof bow moves between extended and retracted positions. In still another aspect of the present invention, a method of operating a convertible roof system is disclosed. The method includes latching an adjustable roof bow in the retracted position, maintaining the roof bow in the retracted position as the convertible top system moves from a stowed position to a raised position and tensioning the cover of the convertible top system by moving the adjustable roof bow to the extended position when the system is in the raised position.